| 摘要 |
PURPOSE:To prevent the output voltage of an inverter from being heightened and prevent a motor from being overheated due to overexcitation, by reducing the conductivity of a semiconductor switch element on a reduced speed mode. CONSTITUTION:By a reduced speed discrimination circuit 28, signal from a comparator circuit 26 or signal from a operation mode production circuit 27 is received, and whether an induction motor 6 is put in a reduced speed mode or not is discriminated, and when the motor 6 is put in the reduced speed mode, then signal is fed to a conductivity change circuit 31. When reduced speed mode signal is received by the conductivity change circuit 31, then the output of voltage command signal for input from a function generator circuit 23, multiplied by a coefficient smaller than 1, to a conductivity arithmetic-operation circuit 24 is generated. Accordingly, the conductivity of a transistor organizing a transistor inverter 5 is reduced, and so by power regenerated when the speed of the induction motor 6 is reduced, intermediate circuit voltage is heightened, and the output voltage of the inverter 5 can be prevented from being heightened. |
